As the microelectronic devices are fabricated in smaller geometries there is an increasing demand for advanced materials that meet the stringent requirements of confined smaller geometries. In particular, sub-micron device geometries have become common place in the fabrication of a variety of liquid crystal displays (LCDs), organic light emitting diodes (OLEDs) and other radio frequency (RD and microwave devices. For example, devices such as radio frequency integrated circuits (RFICs), micro-machine integrated circuits (MMICs), switches, couplers, phase shifters, surface acoustic wave (SAW) filters and SAW duplexers, have recently been fabricated in the sub-micron levels.
With such smaller geometries comes a requirement for dielectric materials with low dielectric constants to reduce or eliminate any cross-talk between adjacent signal lines or between a signal line and a device feature (e.g. a pixel electrode) due to capacitive coupling. Although many low dielectric (low-K) materials are available for microelectronic devices, for optoelectronic devices such materials must also be broadly transparent in the visible light spectrum, not require high temperature processing (greater than 300° C.) that would be incompatible with other elements of such an optoelectronic device, and be both low-cost and feasible for large scale optoelectronic device fabrication.
Thus, it would be desirable to have a material capable of forming a self-imageable layer to avoid the need for depositing a separate imaging layer. Such material should also be easy to apply to a substrate, have a low dielectric constant (3.9 or less) and thermal stability to temperatures in excess of 250° C. Of course, it is also desirable to have such materials available at a lower cost and feature such properties as positive tone or negative photoimaging capability, aqueous base developing capability, high transparency after heat stress and low weight loss at curing temperatures. It has been reported that acrylic polymers, which are inexpensive, offer good photoimaging properties and are aqueous base developable, see for example, Japanese Patent Application Laid-open No. Hei 5-165214 and the radiation-sensitive resin composition comprising an alicyclic olefin resin disclosed in Japanese Patent Application Laid-open No. 2003-162054. Similarly, polyimides have been reported to provide good thermal stability. However, these materials have certain deficiencies and thus making them not so suitable for the applications contemplated herein. For instance, acrylics are not suitable for applications requiring high thermal stability (i.e., temperatures higher than 200° C.), and many of the polyimides in general are not suitable for either positive tone or negative tone formulations requiring aqueous base developability and generally do not exhibit desirable transparency, thus making them unsuitable in certain optoelectronic applications. Although some polyimides have low dielectric constants but still may not have low enough permittivity to be effective in highly integrated and/or miniaturized devices having increased wiring density and high signal speed. One such known polyimide material is the positive tone type photosensitive resin comprising a polyimide precursor and a diazoquinone-type compound disclosed in Japanese Patent No. 3,262,108.
Recently, it has been reported that certain copolymers containing both norbornene-type repeat units and maleic anhydride-type repeat units are useful in certain microelectronic applications featuring self-image forming layer capability, when image-wise-exposed to actinic radiation, see co-pending U.S. patent application Ser. No. 13/550,586, filed Jul. 16, 2012. These compositions are however suitable only for positive tone photoimaging and thermal curing with added additives to the polymeric composition. Thus there is still a need for polymeric compositions which can not only self-crosslink but also can be employed both as positive and negative tone compositions.